Geography A-Level Coastal landscapes

descriptors of landscapes and specific studies. Also structures on questions.

Concordant and Discordant coastlines.

Concordant- coasts are where bands of more-resistant and less-resistant rock run parallel to the coast. 

Discordant- coasts are where the geology alternates between bands of more-resistant rock and less-resistant rocks run at right angles to the coast. 

Concordant and Discordant coastline: Case study + writing

Swanage Bay + Ballard Point —> Southern England

• Headlands and bays are coastal landforms created on discordant coastlines through the combined processes of differential erosion and wave refraction

• Differential erosion erodes soft rock faster, creating landforms, while wave refraction shapes and intensifies headland erosion and bay deposition

• As headlands and bays form, they change the way waves interact with the coast through wave refraction

  • Waves approaching an uneven coastline hit shallower water around the headland first , slowing and bending

  • This concentrates wave energy on the headland's sides and tip

  • Concentrated energy on headland leads to erosional like wave-cut platforms, caves, arches, stacks, and stumps

  • However, bending waves diverge (spread out) and weaken as they enter the bay's larger, deeper areas allowing sand and shingle to form beaches

• Wave refraction changes the amount of energy reaching the shore on a small local scale

Swanage bay - made out of the soft rock clay

Studland bay - made out of the soft rock clay

Ballard point - made of the hard rock chalk

Durlston Head - made of the hard rock limestone.

Erosional Processes

• Abrasion – sediment and stones are picked up by the waves and wear away at the cliff/headland

• Hydraulic action – this is the shear force of the waves forcing air at high pressure into cracks in the cliff; over time, this weakens the rock and causes the joint to widen

• Corrosion – weak acids in seawater dissolve the rock particles

• Attrition – as rocks are moved around by the water, they knock into each other gradually becoming smaller and rounder

Wave-cut platforms

• At high-energy coastlines, hydraulic action and abrasion can cause the formation of wave-cut platforms 

  • Powerful destructive waves attack the base of the cliff at high tide 

  • The hydraulic action and abrasion create a wave-cut notch which, over time, increases in size 

  • This is called undercutting 

  • Eventually, the overhang created by the undercutting collapses due to weathering and gravity 

  • The cliff retreats, leaving a wave-cut platform that is exposed at low tide

A wave cut platform in Portugal

Diagram to show the formation of a wave cut platform 

• At a headland, where the rock is hard, erosion is slow and can lead to a variety of landforms

• Wave refraction concentrates wave energy onto the headland and can contribute to the formation of caves, arches, stacks and stumps

  • Joints in the headland are susceptible to erosion by hydraulic action

  • Over time the joints widen, forming a cave that is enlarged by hydraulic action and abrasion

  • Eventually, erosion cuts through the headland forming an arch

  • The roof of the cave will eventually collapse due to gravity and the lack of support

  • This leaves a stack that will, over time, be eroded by weathering, abrasion, and hydraulic action to form a stump